1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic head for perpendicular magnetic recording that is used for writing data on a (recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, as do magnetic heads for longitudinal magnetic recording, a structure in which a read head having a magnetoresistive element (hereinafter also referred to an MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a pole layer that generates a magnetic field in the direction perpendicular to the plane of the recording medium. The pole layer includes, for example, a track width defining portion having an end located in a medium facing surface that faces toward the recording medium, and a wide portion that is coupled to the other end of the track width defining portion and that is greater in width than the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, as the track width is reduced, the write characteristics, such as overwrite property that is a parameter indicating overwriting capability, suffer degradation. It is therefore required to achieve better write characteristics as the track width is reduced.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits better capability of writing on a recording medium compared with that of the longitudinal magnetic recording system, the occurrence of the skew mentioned above results in problems such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (this phenomenon is hereinafter referred to as adjacent track erasing), and unwanted writing between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
As one of techniques for preventing the above problems resulting from the skew, there is known a technique in which the end face of the track width defining portion located in the medium facing surface is formed into such a shape that the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in, for example, U.S. Pat. No. 6,710,973 B2, U.S. Patent Application Publication Nos. US2003/0151850 A1, and US2006/0077589 A1. In the medium facing surface of a magnetic head, typically, the end farther from the substrate is located forward along the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the shape of the end face of the track width defining portion located in the medium facing surface mentioned above is such that the side closer to the substrate is shorter than the side farther from the substrate.
Consideration will now be given to a method of forming a pole layer in which the end face of the track width defining portion located in the medium facing surface has such a shape that the side closer to the substrate is shorter than the side farther from the substrate, as mentioned above. U.S. Pat. No. 6,710,973 and U.S. Patent Application Publication No. US2003/0151850 A1 each disclose a method including forming a groove in an inorganic insulating film by selectively etching the inorganic insulating film using a mask made of photoresist, and forming the pole layer in this groove. U.S. Pat. No. 6,710,973 discloses that when Al2O3 is used as the material of the inorganic insulating film, BCl3 or a gas mixture of BCl3 and Cl2 is used as an etching gas for etching the inorganic insulating film. U.S. Patent Application Publication No. US2003/0151850 A1 discloses that when Al2O3 is used as the material of the inorganic insulating film, BCl3, a gas mixture of BCl3 and Cl2, a gas mixture of BCl3 and Ar, or BCl3 with CHF3 added thereto is used as an etching gas for etching the inorganic insulating film.
U.S. Patent Application Publication No. US2006/0077589 A1 discloses a method including forming a nonmagnetic conductive layer on a nonmagnetic layer, forming an opening in the nonmagnetic conductive layer by selectively etching the nonmagnetic conductive layer using a mask made of photoresist, forming a groove in the nonmagnetic layer by selectively etching a portion of the nonmagnetic layer exposed from the opening of the nonmagnetic conductive layer by reactive ion etching (hereinafter also referred to as RIE), and forming the pole layer in this groove. U.S. Patent Application Publication No. US2006/0077589 A1 discloses that when Al2O3 is used as the material of the nonmagnetic layer, a gas including a first gas containing Cl or Br and a second gas containing F (fluorine) such as CF4 is used as an etching gas for etching the nonmagnetic layer.
It is known that, as disclosed in U.S. Patent Application Publication No. US2006/0077589 A1, when a nonmagnetic layer made of Al2O3 is selectively etched by RIE using a mask having an opening, the use of an F-containing etching gas makes it possible to taper-etch the nonmagnetic layer such that a groove whose width decreases toward the bottom is formed in the nonmagnetic layer. The reason why the use of an F-containing etching gas makes it possible to taper-etch the nonmagnetic layer made of Al2O3 is that a sidewall-protecting film of AlF3 is formed on the sidewall of the groove when the nonmagnetic layer is etched.
Typically, when a groove whose width decreases toward the bottom is formed in a layer by RIE, the greater is the value of deposition rate of the sidewall-protecting film divided by the etching rate of the groove, the greater is the angle formed by the sidewall of the groove with respect to the vertical direction (this angle is hereinafter referred to as the inclination angle of the sidewall). When a groove is formed in a nonmagnetic layer of Al2O3 by performing RIE with an F-containing etching gas, the inclination angle of the sidewall of the groove can be increased by increasing the deposition rate of the sidewall-protecting film of AlF3, which is achieved by increasing the proportion of the F-containing gas in the entire etching gas.
Conventionally, when a groove for accommodating the pole layer is formed in a nonmagnetic layer by RIE, there are two problems as described below. A first problem is that, when the groove is formed in a nonmagnetic layer made of Al2O3 by performing RIE with an F-containing etching gas, increasing the proportion of the F-containing gas in the entire etching gas in order to increase the inclination angle of the sidewall of the groove results in poor flatness of the sidewall of the groove. This is presumably because the sidewall-protecting film of AlF3 formed in this case is relatively thick and nonuniform. The poor flatness of the sidewall of the groove precludes precise control of the shape of the pole layer to be formed in this groove, and consequently makes it difficult to precisely control the track width and to improve the write characteristics.
A second problem is that, when the groove for accommodating the pole layer is formed in the nonmagnetic layer by RIE, the inclination angle of the sidewall of the groove greatly differs between a portion of the groove to accommodate the track width defining portion of the pole layer and a portion of the groove to accommodate the wide portion of the pole layer. In more detail, when the groove for accommodating the pole layer is formed in the nonmagnetic layer by RIE, if the etching conditions are determined so that a desired inclination angle of the sidewall can be obtained at the portion of the groove to accommodate the track width defining portion of the pole layer, the inclination angle of the sidewall obtained at the portion of the groove to accommodate the wide portion of the pole layer becomes much greater than the desired angle. This is considered to be because of the following. The opening of the mask used for etching the nonmagnetic layer is smaller in width at the portion thereof corresponding to the track width defining portion of the pole layer than at the portion thereof corresponding to the wide portion of the pole layer. As a result, at the portion of the groove to accommodate the track width defining portion of the pole layer, the supply of the etching gas is insufficient and consequently the sidewall-protecting film cannot be sufficiently deposited, which results in a smaller inclination angle of the sidewall. In contrast, at the portion of the groove to accommodate the wide portion of the pole layer, the supply of the etching gas is sufficient and consequently the sidewall-protecting film can be sufficiently deposited, which results in a greater inclination angle of the sidewall.
If the inclination angle of the sidewall becomes much greater than a desired angle at the portion of the groove to accommodate the wide portion of the pole layer, the cross section of the wide portion of the pole layer perpendicular to the direction in which magnetic flux flows will become small in area, which will result in degradation of write characteristics such as overwrite property.
For the above-described reasons, conventionally, in the case of forming a groove in a nonmagnetic layer by RIE and forming a pole layer in this groove, it has been difficult to precisely form such a pole layer that the problems resulting from the skew are prevented and improved write characteristics are provided.